A beaver swimming in a Scottish river. Beavers were hunted to extinction in the UK by the end of the 16th century for their fur, glands for medicine and because their building of dams interfered with other land uses

Proposals to reintroduce this famous wetland engineer to Knapdale Forest in Scotland began in 1994. This was turned down in 2002 and again in 2005. A licence was granted in 2007 and the first beavers to return to Scotland for 400 years will be released this spring. Other proposals for reintroduction in England and Wales are being considered

The large blue butterfly became extinct in the UK in 1975 but was reintroduced to Dartmoor in 2000 from Sweden. This is one of the most vulnerable butterflies in the world. It lays its eggs on wild thyme, then the caterpillars are adopted by red ants who take them into their nests, where the butterfly caterpillars become predators of ant grubs before pupating and emerging as spectacularly bright blue adults

A male great bustard makes a courtship display. Great bustards disappeared from the UK in 1832 after game shooters made it extinct. This emblem of Wiltshire and the heaviest flying bird in the world (it can weigh up to 20kg) was reintroduced to Salisbury Plain in 2004, with eggs rescued from farmland in Russia. Great bustards need open grassland and arable fields where they feed on grasshoppers and cereal seeds

A white-tailed eagle seen in Scotland. In 1700 there were 200 pairs but by 1916 this huge bird, sometimes called the sea eagle, became extinct after persecution in the UK. It was reintroduced to Scotland from Scandinavia in 1975 and there are now 42 breeding territories there. A feasibility study is being carried out on proposals to reintroduce it to East Anglia

A Eurasian lynx mother sits in the grass while her two pups play in their outdoor enclosure in Germany. This secretive, powerful cat with tufted ears and a short tail weighing 25kg survived in Britain until 180AD. The Eurasian lynx is the most likely mammal predator candidate for reintroduction, although many say it is already established in some areas

The last wolf in the UK was killed in Scotland in the 17th century. According to recent population modelling if wolves were reintroduced to Scotland, their population would stabilise at 25 wolves per 1,000 square kilometres

Although wolf populations would have an impact on the high red deer population, experience in other countries shows the wider effect would be to regenerate vegetation and woodland, benefiting wildlife and helping to restore ecosystems